1. Field of the Invention
The present invention relates to a device for radiating an ultrasound-signal into a liquid by means of using an assembly composed of a piezoelectric substrate, a first input-, a second input-, and an output interdigital transducers.
2. Description of the Prior Art
In constructing an acoustical system, a transducer for emitting and detecting an acoustic wave has a key role. A thickness mode piezoelectric transducer is usually used, whose operation frequency is dependent on the thickness of the piezoelectric substrate. Such a conventional type of transducer has a difficulty in high-frequency operation. A surface acoustic wave (SAW) propagates in the form of a leaky wave, when the piezoelectric substrate, sufficiently thicker compared with the wavelength, is in contact with a liquid. In this time, the leaky wave is mode-converted to a longitudinal wave into the liquid. This means that an interdigital transducer (IDT) on the piezoelectric substrate operates at a liquid-solid boundary as a leaky wave transducer for bulk wave radiation into the liquid. The leaky SAW traveling on a sufficiently thick substrate compared with the wavelength has only one mode without velocity dispersion. Thus, conventional transducers such as the thickness mode piezoelectric transducer and the IDT for the leaky SAW have the problem of the limited ultrasound-radiation angle.